Republican Senator John McCain said: "The president has the authority to make this pardon, but doing so at this time undermines his claim for the respect of rule of law as Mr. Arpaio has shown no remorse for his actions."

McCain's junior colleague in the state of Arizona, Jeff Flake, also disagreed with the move.

"I would have preferred that the president honor the judicial process and let it take its course," Flake said in a Twitter post.

Flake has previously been slammed by Trump as "toxic" and "weak" on border issues and crime. His Republican challenger Kelli Ward, who has been strongly endorsed by Trump, said she supports Arpaio's pardon, which could become an issue in the race.

"We applaud the president for exercising his pardon authority to counter the assault on Sheriff Arpaio's heroic efforts to enforce the nation's immigration laws," she said.

The mayor of the city of Phoenix, where Arpaio was sheriff, condemned the pardon in a statement released on Twitter.

Civil rights groups outraged

Civil rights groups largely condemned the pardon as showing a lack of regard for an independent judiciary.

The pardon sent "a dangerous message that a law enforcement officer who abused his position of power and defied a court order can simply be excused by a president who himself clearly does not respect the law," Vanita Gupta, president of the Leadership Conference on Civil and Human Rights and former head of the US Justice Department's civil rights division, said in a statement.

Alejandra Gomez, co-executive director of Living United for Change in Arizona, said: "President Trump pardoned a terrorist tonight. Joe Arpaio intentionally terrorized immigrant communities across Arizona for decades and traumatized an entire generation of Arizonans."

"The only proper place for him is in a jail cell."

Janet Murguia, president of UnidosUS, a Hispanic civil rights and advocacy group, said: "Sheriff Joe Arpaio was the instigator of racial profiling and made official a policy of harassment and abuse based on the color of one's skin."

"Every person of color in this nation has been put in harm's way because of this action and that is unconscionable."

Trump consults Sessions on ending case

The Washington Post reported on Saturday that Trump asked Attorney General Jeff Sessions about dropping the criminal case against Arpaio.